Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Biogeosciences, 6, 1603-1613, 2009
https://doi.org/10.5194/bg-6-1603-2009
© Author(s) 2009. This work is distributed under
the Creative Commons Attribution 3.0 License.
 
11 Aug 2009
Impact of atmospheric and terrestrial CO2 feedbacks on fertilization-induced marine carbon uptake
A. Oschlies IFM-GEOMAR, Leibniz-Institut für Meereswissenschaften, Kiel, Düsternbrooker Weg 20, 24105 Kiel, Germany
Abstract. The sensitivity of oceanic CO2 uptake to alterations in the marine biological carbon pump, such as brought about by natural or purposeful ocean fertilization, has repeatedly been investigated by studies employing numerical biogeochemical ocean models. It is shown here that the results of such ocean-centered studies are very sensitive to the assumption made about the response of the carbon reservoirs on the atmospheric side of the sea surface. Assumptions made include prescribed atmospheric pCO2, an interactive atmospheric CO2 pool exchanging carbon with the ocean but not with the terrestrial biosphere, and an interactive atmosphere that exchanges carbon with both oceanic and terrestrial carbon pools. The impact of these assumptions on simulated annual to millennial oceanic carbon uptake is investigated for a hypothetical increase in the C:N ratio of the biological pump and for an idealized enhancement of phytoplankton growth. Compared to simulations with interactive atmosphere, using prescribed atmospheric pCO2 overestimates the sensitivity of the oceanic CO2 uptake to changes in the biological pump, by about 2%, 25%, 100%, and >500% on annual, decadal, centennial, and millennial timescales, respectively. The smaller efficiency of the oceanic carbon uptake under an interactive atmosphere is due to the back flux of CO2 that occurs when atmospheric CO2 is reduced. Adding an interactive terrestrial carbon pool to the atmosphere-ocean model system has a small effect on annual timescales, but increases the simulated fertilization-induced oceanic carbon uptake by about 4%, 50%, and 100% on decadal, centennial, and millennial timescales, respectively, for pCO2 sensitivities of the terrestrial carbon storage in the middle range of the C4MIP models (Friedlingstein et al., 2006). For such sensitivities, a substantial fraction of oceanic carbon uptake induced by natural or purposeful ocean fertilization originates, on timescales longer than decades, not from the atmosphere but from the terrestrial biosphere.

Citation: Oschlies, A.: Impact of atmospheric and terrestrial CO2 feedbacks on fertilization-induced marine carbon uptake, Biogeosciences, 6, 1603-1613, https://doi.org/10.5194/bg-6-1603-2009, 2009.
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